Process and apparatus for the treatment of semiconductor wafers in a fluid

ABSTRACT

Provided is a process for removing organic materials from semiconductor wafers. The process involves the use of subambient deionized water with ozone absorbed into the water. The ozonated water flows over the wafers and the ozone oxidizes the organic materials from the wafers to insoluble gases. The ozonated water may be prepared in-situ by diffusing ozone into a tank containing wafers and subambient deionized water. Also provided is a tank for the treatment of semiconductor wafers with a fluid and a gas diffuser for diffusion of gases directly into fluids in a wafer treatment tank.

FIELD OF THE INVENTION

The present invention relates to semiconductor manufacturing. Morespecifically, the invention involves an improved process for removingorganic material from wafers during the wet etch/clean steps of waferfabrication. The present invention also relates to an apparatus forcarrying out this process and other processes involving wafer treatmentwith a fluid conducted during semiconductor manufacture.

BACKGROUND OF THE INVENTION

In the fabrication of semiconductor wafers several process steps requirecontacting the wafers with fluids. Examples of such process stepsinclude etching, photoresist stripping, and prediffusion cleaning. Oftenthe chemicals utilized in these steps are quite hazardous in that theymay comprise strong acids, alkalis, or volatile solvents.

The equipment conventionally used for contacting semiconductor waferswith process fluid consists of a series of tanks or sinks into whichcassette loads of semiconductor wafers are dipped. Such conventional wetprocessing equipment poses several difficulties.

First, moving the wafers from tank to tank may result in contamination,which contamination is extremely detrimental to the microscopic circuitswhich the fabrication process creates. Second, the hazardous chemicalsand deionized water which are used have to be regularly replaced withnew solutions, usually introduced to the tank by bottle pour, chemicaldistribution or from building facilities in the case of deionized water.The chemicals generally are manufactured by chemical companies andshipped to the semiconductor manufacturing plant. The chemical purity isthus limited by the quality of the water used by the chemicalmanufacturers, by the container used for shipping and storing thechemical and by the handling of the chemical.

Moreover, as chemicals age, they can become contaminated with impuritiesfrom the air and from the wafers. The treatment of the last batch ofwafers prior to fluid rejuvenation may not be as effective as treatmentof the first batch of wafers in a new solution. Non-uniform treatment isa major concern in semiconductor manufacturing.

Some of the fluid contact steps of semiconductor manufacture includeremoval of organic materials and impurities from the wafer surface. Forexample, in the manufacture of integrated circuits, it is customary tobake a photoresist coating onto a silicon wafer as part of themanufacturing process. This coating of photoresist or organic materialmust be removed after processing.

Generally, a wet photoresist strip process is performed by a solution ofsulfuric acid spiked with an oxidizer of either hydrogen peroxide orozone. This process is referred to in U.S. Pat. Nos. 4,899,767 and4,917,123, issued to CFM Technologies. However, there are manydisadvantages to using a solution of sulfuric acid and an oxidizer tostrip photoresist from wafers during semiconductor manufacture. First,the by-product of the resist strip reaction when hydrogen peroxide isused as the oxidizer is water, which dilutes the concentration of thebath and thereby reduces its ability to strip photoresist. Second, thisprocess operates at a high temperature, generally between 80° and 150°C., typically above about 130° C., which mandates the use of specialheat resistant materials and components in order to house, circulate andfilter the solution, as well as requires extra energy to conduct thecleaning process. Third, the solution is hazardous to handle and disposeof and expensive to manufacture, transport and store.

Moreover, due to the build-up of impurities both dissolved andundissolved in the process bath, the solution must be changedperiodically. Typically, the interval for chemical change out is aboutevery eight hours. Because the chemical adversely affects the drainplumbing, the solution must be cooled to less than about 90° C. prior todisposal. Thus, use of this photoresist stripping process requireseither the use of additional tanks to contain the hot solution or theshut down of the process station during the chemical change period,reducing wafer throughput and increasing cost of ownership.

Finally, after use of a sulfuric acid solution for removal ofphotoresist, the wafers must be rinsed in hot deionized water sincesulfate residues may crystallize on the wafer during processing causingprocess defects.

Another process often utilized for the removal of organic and metallicsurface contaminants is the "RCA clean" process which uses a firstsolution of ammonium hydroxide, hydrogen peroxide, and water and asecond solution of hydrochloric acid, hydrogen peroxide, and water. TheRCA cleaning solutions typically are mixed in separate tanks. The wafersare first subjected to cleaning by the ammonium hydroxide solution, thenare moved to a rinse tank, then to a tank containing the hydrochloricacid cleaning solution, and then to a final rinse tank. This process,like the sulfuric acid process, has the disadvantage of using strongchemicals. Moreover, the wafers are exposed to air during the transfersfrom tank to tank, allowing for contamination. Finally, the use ofperoxide may cause the wafers to suffer aluminum contamination from thedeposition of aluminum in the high pH ammonium hydroxide solution whichis not totally removed in the hydrochloric solution.

Various approaches have been taken to improving the processes andequipment used to treat semiconductor wafers with fluid. These attemptsto improve on present processes generally involve either a change inequipment or a change in the process chemicals.

One approach to eliminating problems with contamination of wafers duringfluid treatment is disclosed in U.S. Pat. Nos. 4,778,532, 4,795,497,4,899,767 and 4,917,123. These patents describe an enclosed full-flowmethod and apparatus which allows the process fluids to flowsequentially and continuously past the wafers without movement oroperator handling of the wafers between processing steps. However, thesepatents still teach the use of hazardous chemicals to perform the fluidtreatment and cleaning of the wafers. Moreover, the equipment needed forthe enclosed apparatus is limited in wafer throughput since all processsequences are performed in the same vessel with concentrated solutions.

U.S. Pat. No. 4,899,767 teaches the use of a separate mixing tank forpreparing the sulfuric acid and oxidizer solution, which solution mustthen be delivered into the treatment tank. The reason for the separatetank is to eliminate the possibility of an explosion due to pressurebuild up from the decomposition of hydrogen peroxide into oxygen andwater.

U.S. Pat. No. 5,082,518, issued to SubMicron Systems, Inc., describes adifferent approach to improving the sulfuric acid and oxidizer processof cleaning semiconductor wafers. The system in this patent provides agas distribution system which includes a sparger plate with diffusionholes for distributing gas throughout the bath in the tank. Thus, ratherthan using a separate tank for mixing as in U.S. Pat. No. 4,899,767, theSubMicron patent provides an apparatus which distributes ozone directlyinto the treatment tank containing sulfuric acid. It has been found,however, that this diffusion system suffers several disadvantages.First, the efficiency of ozone distribution and absorption into thewater is lessened by the large bubbles of ozone produced by theapparatus. The amount of ozone absorbed is important to its ability toreact with the sulfuric acid to remove organic materials from thewafers. Moreover, the type of diffusing element described in U.S. Pat.No. 5,082,518 is believed to not uniformly distribute ozone throughoutthe tank. Finally, as with previous attempts to improve cleaningprocesses for wafers, hazardous chemicals are required, creatinghandling and disposal problems.

An approach to eliminating the problem of the use of hazardous chemicalsis set forth in Ohmi et al, J. Electrochem. Soc., Vol. 140, No. 3, March1993, pp. 804-810, which describes the use of ozone-injected ultrapurewater to clean organic impurities from silicon wafers at roomtemperature. However, this process also suffers several disadvantages.Ohmi et al provides only a process for the removal of a very thin layerof organic material, i.e., a layer of surfactant left from thelithography process. The process described by Ohmi et al could notremove photoresist in a reasonable time frame. The process was intendedfor, and works on organic contamination layers of less than 50Angstroms. It is too slow to work on organic contamination layers of50-250 mils. Thus, a process which can quickly and effectively removeorganic materials of all thicknesses from semiconductor wafers withoutthe use of hazardous chemicals is still not available in the art.

A process for the removal of organic materials during semiconductormanufacture which can avoid the foregoing problems while providingeffective removal of organic materials would be of great value to thesemiconductor industry. Further, an apparatus for conducting such aprocess which eliminates the need for multiple tanks would also be ofgreat value to the industry.

Accordingly, it is an object of the present invention to provide aprocess for the removal of photoresist or other organic materials fromsemiconductor wafers which does not use hazardous chemicals.

It is still another object of the present invention to provide a processwhich does not require cool down tanks or idle stations due to chemicalchange out.

It is still another object of the present invention to provide a systemfor the fluid treatment of semiconductor wafers in which more than onetreatment can be conducted without moving the wafers to a separate tank.

These and other objects of the present invention will become apparentupon a review of the following specification and the claims appendedthereto.

SUMMARY OF THE INVENTION

The foregoing objectives are achieved by a process for removing organicmaterials from semiconductor wafers comprising contacting the waferswith a solution of ozone and water at a temperature of about 1° to about15° C. The wafers are preferably contacted with the solution for a timesufficient to oxidize the organic materials from the wafers.

In another embodiment of the invention, a process for removing organicmaterials is provided comprising placing semiconductor wafers into atank containing deionized water, diffusing ozone into the deionizedwater for a time sufficient to oxidize the organic materials from thewafers, maintaining the deionized water at a temperature of about 1 toabout 15° C., and rinsing the wafers with deionized water. In apreferred embodiment, the organic material removed is photoresist.

In another embodiment of the invention, a process for removing organicmaterials from semiconductor wafers is provided comprising placingsemiconductor wafers into a tank containing deionized water, diffusingozone into the deionized water, simultaneously exposing the ozone toultraviolet light as the ozone is absorbed and bubbled through thedeionized water to form oxygen free radicals and oxygen molecules whichoxidize the organic material to insoluble gases, maintaining thedeionized water at a temperature of about 1° to about 15° C., andrinsing the wafers with deionized water.

The objects of the invention are further achieved by a tank fortreatment of semiconductor wafers with a fluid comprising meansconnected to the tank for providing fluid into the tank, means forsupporting at least one wafer within the tank in contact with the fluid,means connected to the tank for injecting gas into the tank, and meansfor diffusing the gas into the tank such that the gas is absorbed intothe fluid and contacts the surface of each wafer disposed in the tank.The means for diffusing comprises a composite element having a permeablemember and a nonpermeable member, the permeable member having a topportion and a bottom portion, a means defining an open space in a centerportion of the permeable member, and a means defining a trenchpositioned on the top portion of the permeable member between an outerperiphery of the permeable member and the means defining an open space.The impermeable member has a means defining an open space in a centerportion of the impermeable member which corresponds to the meansdefining an open space in a center portion of the permeable member. Thepermeable member and the impermeable member are joined such that thetrench opens at the top portion of the permeable member and is coveredby the impermeable member. The composite element is positioned with thebottom portion of the permeable member connected to the bottom of thetank.

In a preferred embodiment, the tank comprises a first side and a secondside, the first side of the tank having a vertical portion at a topportion of the tank and an inwardly tapered portion at a bottom portionof the tank, the tapered portion being longer than the vertical portion,and a second side of the tank having a vertical portion at a top portionof the tank and an inwardly tapered portion at a bottom portion of thetank, the tapered portion being shorter than the vertical portion.

The objects of the invention are further achieved by the gas diffuser ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a cross-section of a side view of anapparatus for the treatment of semiconductor wafers with fluid accordingto the present invention.

FIG. 2 is a schematic diagram of a cross-section of a front view of thetank of the present invention.

FIG. 3 is an exploded three-dimensional schematic diagram of a preferredembodiment of the gas diffuser of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The process of the present invention eliminates the need to usehazardous chemicals in the removal of organic materials fromsemiconductor wafers during the manufacturing process. Although ozonehas little solubility in deionized water at room temperature or highertemperatures, Applicant has surprisingly discovered that ozone diffusedthrough a subambient deionized water solution will quickly andeffectively remove organic materials such as photoresist from waferswithout the use of other chemicals. Although unexpected, it is believedthat lowering the temperature of the solution enables a sufficientlyhigh ozone concentration in solution to provide oxidization ofsubstantially all of the organic material on the wafer to insolublegases.

In photoresist removal, the process of the invention results inoxidation of the organic materials present to insoluble gases such asCO_(x) and NO_(x). These gases bubble out of solution and are exhaustedfrom the system, usually into a hood or other exhaust apparatus.

In order to obtain the sufficiently high ozone concentration in thedeionized water, the bath typically is maintained at about 1° to about15° C. Below about 1° C., ice may form in the tank. Since thesesemiconductor process tanks are typically made from quartz, the ice maycause the quartz to break and prohibit movement of silicon wafers intoand out of the process vessel. In addition, the system will not functionsince the water has changed physical states from a liquid to a solid andcannot absorb gases uniformly Above 15° C. a sufficient amount of ozonemay not be absorbed into the deionized water to remove the organicmaterial on the semiconductor wafers in a timely fashion. In a preferredembodiment, the bath is about 5° C. to about 9° C.

The appropriate temperature can be maintained by any means known tothose of skill in the art, including cooling the bath itself or,preferably, by continually supplying the bath with fresh, subambientdeionized water. In a preferred embodiment, the water is used as aprocess chemical and all or a portion of the water is passed through achiller prior to entering the treatment zone.

The wafers may be placed directly into a tank containing chilledozonated water or, preferably, the wafers are placed in a tank ofdeionized water and ozone is diffused into the tank. Preferably, theozone is diffused into the subambient water solution for a timesufficient to oxidize substantially all of the organic materials on thewafers. The amount of time needed for diffusion of the ozone into thewater will depend on the nature of the organic material being removedand the amount of that material. The specific temperature of the waterbath will also affect the time for diffusion of ozone since the amountof absorption of ozone into the water is dependent on the temperatureand the oxidation power of the water solution is dependent on the amountof ozone absorbed.

Generally, the ozone will be diffused into the deionized water for about1 to about 15 minutes. In a preferred embodiment, the ozone is diffusedinto the deionized water for about 5 to about 10 minutes.

In an alternative embodiment, ozone is diffused into the water solutionand exposed to ultraviolet radiation from an ultraviolet light source inorder to produce oxygen free radicals and oxygen molecules which oxidizethe organic material or photoresist on the wafers.

After the ozone in the water solution sufficiently oxidizes the organicmaterial, the wafers are rinsed with fresh deionized water for about 1to about 5 minutes. This rinse step generally will be at ambienttemperature. In a preferred embodiment of the invention, the wafers arerinsed a second time with deionized water heated from about 65° C. toabout 85° C. in order to remove water soluble metals, such as sodium andpotassium, from the surface of the wafers. The alkali and alkali earthmetals originate from contaminates in the photoresist.

The removal of the organic material by the process of the invention cantake place in any type of wafer bath or wafer cleaning apparatus.However, the ozonated water process of the present invention operates byoxidizing the photoresist or other organic material upon ozone contactwith each wafer in solution. Therefore, the ozone must be dispersed inthe tank in such a manner that each wafer is contacted by ozone.

Unlike the sulfuric acid process where the resist is lifted off thewafer and digested in the chemical (oxidized), the ozonated waterprocess of the present invention does not lift resist from the wafer,but oxidizes the photoresist only upon ozone contact with the wafer. Ifthe ozone is not properly dispersed in the tank or the wafers areshielded due to wafer containment vessels, the resist will not beremoved. Thus, it is preferable that the ozone is present in the tanksuch that it is sufficiently absorbed into the water and uniformlycontacts the face of each wafer in the treatment zone. With this method,there is direct oxidation of the organic photoresist to insoluble gases,eliminating the problem of particle build up within the bath and theneed for filtration equipment.

In a preferred embodiment, the process of the invention is conducted inthe apparatus of FIG. 1. Processing takes place in a hooded, exhaustedwet station, with proper ozone monitoring and catalytic destructequipment in place. Resisted wafers or other wafers from which organicmaterials are to be removed are introduced into process tank 13 filledwith subambient deionized water (1°-15° C.). The tank operates in a lowflow (about 0.5 gpm) cascade mode, with water feed line 7 runningthrough chiller 8 during processing in order to supply a continuousstream of chilled deionized water. Ozone from the ozone generator 6 isthen diffused through conduit 5 into the tank through an in-situdiffuser 4. The resist strip is timed, after which the ozone is turnedoff and the wafers are rinsed by the continuous high flow (about 10-15gpm) of deionized water. The drain line 12 is diverted to deionizedwater reclaim 10, and fresh deionized water is activated for the rinse.After a timed ambient deionized water rinse, the wafers may optionallyreceive a hot deionized water rinse.

In a particularly preferred embodiment of the invention, the process isconducted in the tank of FIG. 2 which contains the gas diffuser of FIG.3. However, although the apparatus of FIG. 1, the tank of FIG. 2 and thegas diffuser of FIG. 3 of the present invention are particularlypreferred for use with the ozonated water process of the presentinvention, they may also be used for conducting any fluid treatment ofsemiconductor wafers. Specifically, previously known methods of removingorganic materials from wafers may be used in the apparatus and tank ofthe invention. Applicant has found that the apparatus of the presentinvention can be used to efficiently carry out previously knownprocesses without the need for multiple tanks. Moreover, the apparatusof the present invention provides the ability to generate chemicalsin-situ, avoiding the problem of aging chemicals or transfer ofhazardous chemicals from remote locations.

The preferred apparatus for treatment of semiconductor wafers with afluid includes a tank for use in a hooded, exhausted wet station. Thetank generally will have means connected to the tank for providing fluidinto the tank, means for supporting at least one wafer within the tankin contact with the fluid, means connected to the tank for injecting gasinto the tank, and means for diffusing the gas into the tank such thatthe gas is absorbed into the fluid and contacts the surface of eachwafer disposed in the tank.

FIG. 1 illustrates a preferred embodiment of the claimed invention. Thetank 13 holds the fluid to be used to treat semiconductor wafers.

The means for providing fluid to tank 13 generally will be a conduitconnected to the tank, but any device or apparatus known to those ofskill in the art for providing a flow of fluid to a tank may beutilized. Fluid can be provided to the tank, for example, byperfluoroalkoxylvinylether (PFA) tubes or pipes, polytetrafluoroethylene(PTFE) tubes or pipes, polyvinylidene fluoride (PVDF) tubes or pipes, orquartz tubes. Preferably, PFA tubes or pipes are utilized. In apreferred embodiment, PFA tubes are connected to the tank with a flaredfitting connection.

In the preferred embodiment shown in FIG. 1, the means for providing afluid is through feed line 7 at the bottom of the tank, with the fluidflowing in an upwardly direction into tank 13. Generally, the tank willbe operated on a continuous overflow basis, so that as the fluid flowsupward from the means for providing fluid and reaches the top of thetank, the fluid will overflow out of the tank into overflow weir 1allowing for fresh fluid to be introduced at the bottom of the tank.This method of introducing and removing fluid from a treatment tank iswell known in the semiconductor manufacturing art.

From overflow weir 1, fluid is fed into return line 12. A three wayvalve 11 operates to either recirculate the fluid by way of line 9 ordrain the fluid through drain line 10.

The means for injecting a gas into the tank can be any means known tothose of skill in the art for providing a gas to a tank for treatment ofsemiconductor wafers. The gas can be plumbed to the diffuser, forexample, with either a PFA tube or a PTFE tube or pipe. Preferably, PFAtubing with a flared fitting is used to inject the gas into the tank.

FIG. 1 shows the means for injecting a gas into the tank at 5 which isconnected to the tank at the bottom of the tank, below the means fordiffusing the gas into the tank. Conduit 5 feeds directly into diffuser4 to provide a uniform flow of gas to the tank.

The means for supporting at least one wafer within the tank in contactwith the fluid (shown in FIG. 2) can be any means known to those ofskill in the art for placing a wafer in contact with a treatmentsolution. Wafer boats and cassettes useful for this purpose are wellknown.

Preferably, when the ozonated water process of the invention is to becarried out in the tank, the boat or cassette will allow uniform fluidflow across each wafer in the tank. In a preferred embodiment, forpurposes of allowing the maximum freedom of fluid flow across thewafers, a cassetteless system of supporting the wafers in the tank isutilized. A preferred support system is by the use of four rod endeffector 15 (FIG. 2) which allows the wafer to be contacted in only twopoints by the support. FIG. 2 shows the end view of the four rails ofthe support attached to an end plate. The points of contact are at the 5and 7 o'clock positions and the depth of the wafer groove is no greaterthan about 2 mm. In the most preferred embodiment, the wafer supportsystem securely supports the silicon wafers at a slight angle withuniform spacing between the wafers.

The means for diffusing a gas can be any means which provides finebubbles of ozone or other gases into the tank and uniformly distributesthe gas throughout the tank, ensuring that each wafer is contacted bythe gas absorbed into the fluid. Preferably, the bubbles which areprovided by the diffuser are initially about 25 to about 40 microns indiameter.

The means for diffusing a gas can be utilized to deliver any gas to thetank to be used in a fluid treatment, such as hydrochloric gas, ammonia,hydrofluoric gas, chlorine gas or bromine. These gases can be sentthrough the diffusing means either individually or in combinations withor without ozone to effect different chemistries in the process tank.

Preferably, the means for diffusing a gas comprises a composite elementhaving a permeable member and a nonpermeable member. The permeablemember has a top portion and a bottom portion, a means defining an openspace in a center portion of the permeable member, and a means defininga trench positioned on the top portion of the permeable member betweenan outer periphery of the permeable member and the means defining anopen space. The impermeable member has a means defining an open space ina center portion of the impermeable member which corresponds to themeans defining an open space in a center portion of the permeablemember. The permeable member and the impermeable member are joined suchthat the trench on the top portion of the permeable member is positionedbetween the permeable member and the impermeable member. The compositeelement is preferably positioned with the bottom portion of thepermeable member connected to the bottom of the tank. Thus, thepermeable portion of the composite element faces toward the bottom ofthe tank and the impermeable portion of the composite element facestoward the top of the tank. The open portion of the trench is betweenthe two members on the inside of the composite element.

Gas diffuser 4 of the present invention operates by allowing gasreceived into the diffuser to diffuse through the pores of the permeablemember into the fluid solution. The gas first flows into the trenchportion of the permeable member since that area offers the leastresistance to the flow of gas. As the gas pressure increases, the gaswhich has flowed into the trench diffuses through the pores of thepermeable member out into the tank. Since the impermeable member on topof the permeable member prevents the flow of gas out the top of thediffuser, the gas diffuses out the bottom and sides of the diffuser,flowing downward. When the means for providing fluid is at the bottom ofthe tank, this downward flow of the gas is countercurrent to the flow offluid, allowing for excellent absorption of the gas into the fluidflowing upwardly into the tank.

It is desirable for the diffuser to be hydrophobic to prohibit waterbackstreaming into the gas lines which may lead to metal corrosion atthe gas regulation box. Moreover, the diffuser should be chemicallycompatible with ozone and chemically pure to avoid entrainment ofcations, anions or particles into the process bath.

The gas diffuser preferably is made from a mixture ofpolytetrafluoroethylene (PTFE) and perfluoroalkoxylvinylether (PFA). Byvarying the temperature and pressure under which the mixture is preparedby methods known in the art, both porous and nonporous members areformed. The impermeable and permeable members are preferably comprisedof about 95% PTFE and about 5% PFA. The permeable member and theimpermeable member may be joined by any number of methods as long as theresult is a composite member that will not come apart under the stressesin the tank. Preferably, the members are heat sealed together,essentially melting or fusing the members together using carbon-carbonbonds.

Once the permeable member is formed, a trench is bored out of the PTFEin the top portion of the member. The resulting diffuser has on theorder of about 100,000 pores of a size of about 25 to about 40 micronsin diameter through which gas may permeate into the treatment tank. Theuse of the trench in the diffuser allows the gas to diffuse into thetank as very fine bubbles which can be easily absorbed into the fluidand uniformly distributed throughout the tank.

A diffuser according to a preferred embodiment of the invention is shownin FIG. 3. Impermeable member 30 is the top portion of the compositeelement. Permeable member 31 is the bottom portion of the compositeelement which has trench 32 bored out of it to provide uniformdistribution of the gas throughout the tank. The preferred rectangularconfiguration of the diffuser is as shown in FIG. 3. However, differentconfigurations may be used such as parallel rods for square orrectangular tanks or circular diffusers for round or cone-shaped tanks.In a preferred embodiment, the diffuser is about one-quarter the area ofthe bottom of the tank.

The diffuser sits at the bottom of the tank and may be attached to thetank by any appropriate means. Preferably, the diffuser is attached tothe tank utilizing unused end plugs. The plugs are inserted into thediffuser first and then the entire assembly is mounted in the tank.Conduit 5 feeds gas directly into the diffuser from the bottom of thetank. This enables the gas to enter the trench and then diffuse out thebottom and sides of the permeable member in a uniform manner.

The tank of the preferred embodiment is shown in FIG. 2 (labelscorrespond to FIG. 1), further illustrating wafer 14 held by preferredsupport 15 in tank 13. Tank 13 has at least two sides with inwardlytapered portions for reducing the volume of chemicals which are requiredfor treatment of the wafers. One of the sides has a vertical portion atthe top of the tank and an inwardly tapered portion at the bottom of thevessel with the tapered portion longer than the vertical portion and asecond side of the tank has a vertical portion at the top of the tankand an inwardly tapered portion at the bottom of the vessel with thetapered portion shorter than the vertical portion. This tank structurereduces the volume of chemicals used during treatment by about 27% andallows for a quick turn-over in the chemical composition of the solutionin the tank.

The structure of tank 13 also provides advantages when using megasonictransducers. Tank 13 may have one or more megasonic transducers 2mounted thereon for agitation of the solution. The transducers arepreferably oriented between perpendicular and 30° off perpendicular tothe gas stream with the wafers oriented parallel to the megasonic beam.

The megasonics in a preferred embodiment are mounted on the side of thetank with the longer taper. Opposite this side is a shorter taperedside. The sides are tapered to accomplish two functions. The first is toinsure the megasonic power does not reflect off the far wall and returnto the transducers. Such reflected energy would result in burning up thetransducers and thereby lead to a short component lifetime. The secondreason for the choice of the tapered walls is to pass the megasonicpower through the zone where the volume of silicon wafers is to beprocessed and use the reflected beam off the far wall to make a secondpass through the zone of silicon wafers. In doing so, each megasonicpulse has two passes through the wafers to increase the particle removalefficiency.

Tank 13 may also be fitted with ultraviolet light source 3 forsubjecting the solution to UV radiation. The UV source can be mounted onthe outside of the tank or, preferably, is submerged into the tank andplaced over diffuser 4, as shown at 3 in FIG. 1 and FIG. 2. The UV lightcan be utilized to generate oxygen free radicals and oxygen moleculesfrom ozone bubbled directly into the treatment tank for removal oforganic materials on wafer 14 during operation of the ozonated waterprocess of the invention.

In a further embodiment, the tank is fitted with a lid for closing thetank which has an infrared light source mounted in the lid. The infraredlight may be used to aid in drying the wafers after treatment. Theinfrared light source is disposed in the lid such that the light sourceis above the fluid in the tank when the lid is closed and is directeddownward into the fluid. In a preferred embodiment, the IR light is usedin conjunction with a solvent drying process wherein an appropriatehydrocarbon solvent is introduced on the top of the fluid in the tankand the wafers are slowly lifted through the solvent layer so that thesolvent layer displaces the water from the wafers. Any solvent remainingon the wafers is vaporized by the process of heating the wafers usingthe IR lamp to about 150° C.±30° C. and introducing ozone gas to oxidizethe organic remnants. Other methods of drying the wafers are known inthe art and use of any such methods are contemplated by the invention.

While the apparatus for treatment of semiconductor wafers with fluids,the tank and the diffuser discussed herein are preferably used with theozonated water process of the present invention, the structure providedis also useful with a number of other treatment processes. The apparatusprovided eliminates the need to use multiple tanks by providing a meansto generate chemicals in-situ so that several steps of a process may beconducted in one tank without moving the wafers. Thus, the diffuser maybe used to introduce any gases into the tank needed for fluid treatmentor for formation of fluids for treatment of semiconductor wafers. One ofordinary skill in the art is familiar with the tank materials neededwhen using various gases.

For example, both the sulfuric acid cleaning process and the RCAcleaning process described above can be conducted in the presentapparatus quickly and efficiently without the need for multiple tanks orseparate mixing tanks.

For the sulfuric acid process, acid enters a tank through a deliverytube in the weir, so that the acid goes to filtration first beforeentering the process area of the tank. Delivery of acid from arecirculating unit is through the bottom of the tank. After wafers withphotoresist are introduced to the process area of the tank, ozone isdiffused into the tank while megasonic transducers are activated. Theother configuration of the sulfuric acid clean using ozone is to diffuseozone (O₃) into the tank through the diffuser with the resisted waferspresent, then activate the UV light. The UV light will generate theoxygen free radical to react directly with the organic matter on thesilicon wafers and to act as an oxidant which reacts with the sulfuricacid to form the traditional Caro's Acid which reacts with thephotoresist. This reaction is simultaneous with the sonic energy of thedual frequency transducers.

For the RCA clean, the tank operates in overflow mode. Deionized watercascades continuously at a variable flow rate (0.5, 1, 5 and 10 gpm), orthe tank is in static mode. The wafers are first rinsed, then the watercascade is turned off. Ozonated water is generated in the tank and/or ispumped into the tank and then the ammonia gas (NH₃) is diffused into thetank to create the SC1 solution. Optionally, ozone in conjunction withUV radiation may be used to generate the oxygen free radical. Themegasonic transducers are activated, operating in dual frequency modeand firing alternately in order to prevent overheating of the crystals.After processing, the water cascade is turned on to flush (from thebottom of the tank) the SC1 solution from the tank. The waterflush/rinse is timed and the drain may also have a resistivity monitorin-line. When the tank and wafers are rinsed, the water line switches tohot deionized water to elevate the temperature in the process tank. Whenthe tank temperature reaches 70° C., the overflow is turned off and thetank returns to static mode. Ozone gas is then diffused into the tank,followed by hydrochloric gas, to create the SC2 solution. Optionally,ozone in conjunction with UV radiation may be used to generate theoxygen free radical. The megasonic transducers are activated. Afterprocessing, the water cascade is turned on to flush the tank and rinsethe wafers based on time and resistivity. A final rinse is performedwith hot deionized water based on time.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention, and it should be understood that thisinvention is not to be unduly limited to the illustrative embodimentsset forth herein.

What is claimed is:
 1. A process for removing organic materials fromsemiconductor wafers comprising contacting the wafers with a solution ofozone and water at a temperature of about 1° C. to about 15° C.
 2. Theprocess of claim 1, wherein the organic material is photoresist.
 3. Theprocess of claim 1, wherein the temperature is about 5° C. to about 9°C.
 4. A process for removing organic materials from semiconductor waferscomprising:placing semiconductor wafers into a tank containing deionizedwater; diffusing ozone into the deionized water for a time sufficient tooxidize the organic materials from the wafers to insoluble gases;maintaining the deionized water at a temperature of about 1° C. to about15° C.; and rinsing the wafers with deionized water.
 5. The process ofclaim 4 further comprising exhausting the insoluble gases from the tank.6. The process of claim 4, wherein the ozone is diffused uniformlyacross the face of each wafer in the tank.
 7. The process of claim 4further comprising, after the rinse with deionized water, rinsing thewafers with deionized water heated to a temperature between about 65° C.and about 85° C.
 8. The process of claim 4, wherein ozone is diffusedinto the deionized water for about 1 to about 15 minutes.
 9. The processof claim 8, wherein the wafers are rinsed for about 1 to about 5minutes.
 10. The process of claim 4, wherein the organic material isphotoresist.
 11. The process of claim 4, wherein the deionized water isat a temperature of about 5° C. to about 9° C.
 12. A process forremoving organic materials from semiconductor wafers comprising:placingsemiconductor wafers into a tank containing deionized water; diffusingozone into the deionized water; simultaneously with diffusing the ozoneexposing the ozone to ultraviolet light as the ozone is absorbed andbubbled through the deionized water to form oxygen free radicals andoxygen molecules which oxidize the organic materials to insoluble gases;maintaining the deionized water at a temperature of about 1° C. to about15° C.; and rinsing the wafers with deionized water.
 13. The process ofclaim 12, wherein the organic material is photoresist.
 14. The processof claim 12, wherein the insoluble gases are exhausted from the tank.15. A process for removing organic materials from semiconductor waferscomprising a stripping of the wafers effected by contacting said waferswith a solution of ozone and water at a temperature of about 1° C. toabout 15° C.
 16. The process for removing organic materials fromsemiconductor wafers of claim 15, wherein said stripping removes a layerof organic materials having a thickness from about 50 to about 250 mils.17. The process for removing organic materials from semiconductor wafersof claim 15, wherein said stripping is not preceded by a strippingtreatment of alkali or acid reagents.
 18. The process for removingorganic materials from semiconductor wafers of claim 15, wherein saidstripping is not preceded by a stripping treatment of organic solvent.19. The process for removing organic materials from semiconductor wafersof claim 15, wherein said stripping is not preceded by removal oforganic materials from said semiconductor wafers.